All synthetic fibers, including polyester fibers, can be classified into two groups, namely (1) continuous filaments and (2) fibers that are discontinuous, which latter are often referred to as staple fibers or cut fibers. This invention provides improvements relating to the processing of the latter group, but such polyester staple fibers have first been formed by extrusion into continuous polyester filaments, which are processed in the form of a tow of continuous polyester filaments.
This invention provides a new tow of continuous polyester filaments that provides advantages in being capable of better processing downstream on the worsted system.
Mostly, the objective of synthetic fiber producers has been to replicate advantageous properties of natural fibers, the most common of which have been cotton and wool fibers. Most of the polyester cut fiber has been blended with cotton. A typical spun textile yarn is of cotton count 25, and of cross-section containing about 140 fibers of 1.5 dpf (denier per filament) and 1.5 inch length. Polyester/worsted yarns are different, typically being of worsted count 23, and of cross-section containing about 60 fibers for single yarn and about 42 fibers for bi-ply yarn, with fibers that have been of 4 dpf and 3.5 inch length. The yarn count may vary over 55 worsted to 10 worsted, while the denier and length may vary up to about 4.5 and down to about 3. It is only relatively recently that the advantages of using synthetic fibers of dpf lower than the corresponding natural fibers (such as wool) have been found practical and/or been recognized. Recent attempts to provide low dpf polyester fiber for blending with wool on the worsted system have not, however, been successful, and require improvement. As the fiber denier has been reduced, the fibers have become harder to process (carding, drafting, gilling, etc.) in the mill. In fact, below a certain fiber denier, the polyester fibers that I have tried have been practically impossible to process, and/or have given poor quality fabrics. Thus, for commercially-acceptable processing and blending with wool in practice, I have found that the fiber denier of such polyester fibers has had to be a minimum of about 3 dpf. Tows of (nominal) dpf less than 3 are not believed available commercially at this time. This has been the status so far in the trade. Thus far, trying to manipulate a desire to reduce dpf has appeared to be contradictory or incompatible with satisfactory mill processibility.
Processing on the worsted system is entirely different from most practice currently carried out on the cotton system, which generally uses cotton fiber that is sold in bales and that may be mixed with polyester fiber that is primarily staple or cut fiber, that is also sold in compacted bales. In contrast, for processing on their system, worsted operators want to buy a tow of polyester fiber (instead of a compacted bale of cut fiber) so they can convert the tow (which is continuous) into a continuous sliver (a continuous end of discontinuous fibers, referred to hereinafter shortly as "cut fiber") by crush cutting or stretch-breaking. This sliver is then processed (as a continuous end) through several stages, i.e., drafting, dyeing, back-washing, gilling, pin-drafting and, generally, finally blending with wool. It is very important, when processing on the worsted system, to maintain the continuity of the sliver. Also, however, it is important to be able to treat the cut fiber in the sliver appropriately while maintaining a reasonably satisfactory processing speed for the continuous sliver. As indicated, recent attempts to use desirable polyester tow, e.g., with low dpf, have not produced desired results. For instance, unsatisfactorily low machine productivity rates have been required after dyeing; I believe this may have been because such polyester fiber has previously packed together too tightly.